Gypsum

Gypsum is a soft sulfate mineral composed of Calcium sulfate dihydrate (CaSO4:2H20). It is widely used as a fertilized, in sculptures and as plaster material. Gypsum is a chalk like material and is very light in weight. It is available in crystalline form in nature. In recent years, the construction sector has witnessed a number of new trends, technology advancements and innovations across applications, all aimed at making construction faster and delivering higher performance. Gypsum although a much older material than the cement & sand plaster has rarely been used extensively in construction industry. Now a days, Gypsum has proved to be a miraculous material aiding interior construction due to its properties.

What is Gypsum Plaster?

When dry POP powder is mixed with water it hardens. This material which can be applied over brick, block or concrete surface to form a smooth surface is called gypsum plaster.

Earlier, a 6 mm coat of gypsum plaster (termed as POP punning) is usually applied on the top of cement plaster to give a smooth finish to it before painting. This is a two stage process and involves various elements like sand, cement and water which has to be mixed onsite. This process is slowly being replaced by a direct application of single coat of gypsum plaster. In gypsum plaster, readymade POP powder is mixed with water and applied directly on the wall.

Gypsum Plaster can be applied directly on any brick, solid or hollow blocks, AAC blocks and plaster boards. Gypsum plaster has good insulation properties, fire resistant and impact resistant. Also, gypsum saves a lot of time during construction and has superior finish. These properties have clearly drawn attention of real estate builders and contractors towards choosing gypsum plaster over traditional cement plaster.

Gypsum Plaster advantages disadvantage

Advantages of Gypsum Plaster

Contractors and Builders started preferring gypsum plaster instead of due to its superior finish and time saving attributes. Some of the advantages of gypsum plaster are:

• Ease of Application (Workability): Gypsum can be directly applied over brick/block work without separate finishing. It is also very easy to apply and level gypsum plaster.

• No Shrinkage Cracks: Gypsum reaction produces less heat as compared to cement reaction with water. So there are fewer Shrinkage cracks in gypsum plaster as compared to traditional cement plaster

• Quick Setting Time: Gypsum sets quickly (i.e., within 25-30 mins). So painting could be started 72 hours after application of gypsum plaster. Plaster has to be dried up before painting.

• No curing time required: Unlike Traditional Cement Plaster, Gypsum plaster doesn’t need any curing saving water and time during construction

• High Productivity: Reduces time considerably when compared to conventional cement plaster

• High Performance: Excellent high strength after drying, Durable and Light weight (Reduces dead load on structure)

• Smooth Finish: Perfectly lined, levelled, smooth walls and perfect right angled corners

• Reduced Supervision: Careful quality checking is required for cement plaster as cement and sand has to be properly proportioned. In contrast, gypsum plaster doesn’t require same amount of quality checks for application thus reducing supervision efforts.

• Readily available raw materials: Gypsum is a ready available material. Natural Sand, which is a raw material used in Traditional cement plaster, is hard to obtain.

• Fire resistant: Gypsum plaster is highly resistant to fire.

• Low thermal conductivity: Gypsum has low thermal conductivity. This saves electrical cost for heating and cooling rooms in a building.

• Decorative application: It can be easily applied to decorative purposes also and can be molded into different shapes

Disadvantages of Gypsum Plaster

Gypsum plaster cannot be used for outside walls since they retain dampness. Also gypsum plastering cannot be done in areas which are continuously damp such as bathrooms etc. Gypsum plaster is costlier than traditional cement motar plaster (cement and sand) for same thickness of plaster. But in areas where natural/river sand is not available for construction, cement mortar plastering would require a 6 mm gypsum layer to finish it making cement plaster more costly.

Storage of Gypsum Plaster At Site

Exposure to water or moisture reduces the setting time and strength of gypsum plaster. So gypsum has to be stored properly. Gypsum Plaster (POP) bags has to be stored on elevated surface (dry platform) made of bricks/timber/concrete at site. The minimum shelf life of Gypsum Plaster 3-4 months from the date of manufacture. But if properly stored gypsum can be use in excessive of 6 months subject to temperature and humidity.

Varieties of Use in many industries

Construction industry

• Gypsum board is primarily used as a finish for walls and ceilings, and is known in construction as plasterboard, sheet rock, or drywall.

• Gypsum blocks are used like concrete blocks in building construction.

• Gypsum mortar is an ancient mortar used in building construction.

• A component of Portland cement used to prevent flash setting (too rapid hardening) of concrete.

Agriculture

• Fertilizer: In the late 18th and early 19th centuries, Nova Scotia gypsum, often referred to as plaster, was a highly sought fertilizer for wheat fields in the United States. Gypsum provides two of the secondary plant macronutrients, calcium and sulfur. Unlike limestone, it generally does not affect soil pH.

• Reclamation of saline soils, regardless of pH. When gypsum is added to sodic (saline) and acidic soil, the highly soluble form of boron (sodium metaborate) is converted to the less soluble calcium metaborate. Exchangeable sodium percentage is also reduced by gypsum application. The Zuiderzee Works uses gypsum for the recovered land.

• Other soil conditioner uses: Gypsum reduces aluminium and boron toxicity in acidic soils. It also improves soil structure, improving water absorption and aeration.

• A wood substitute in the ancient world: For example, when wood became scarce due to deforestation on Bronze Age Crete, gypsum was employed in building construction at locations where wood was previously used.

• Soil water potential monitoring: a gypsum block can be inserted into soil, its electrical resistance measured to derive soil moisture.

Modeling, sculpture and art

• Plaster for casting moulds and modeling.

• As alabaster, a material for sculpture, it was used especially in the ancient world before steel was developed, when its relative softness made it much easier to carve. During the Middle Ages and Renaissance, it was preferred even to marble.

• In the medieval period, scribes and illuminators used it as an ingredient in gesso, which was applied to illuminated letters and gilded with gold in illuminated manuscripts.

Food and drink

• A tofu (soy bean curd) coagulant, making it ultimately a significant source of dietary calcium.

• Adding hardness to water used for brewing.

• Used in baking as a dough conditioner, reducing stickiness, and as a baked-goods source of dietary calcium. The primary component of mineral yeast food.

• Used in mushroom cultivation to stop grains from clumping together.

Medicine and cosmetics

• Plaster for surgical splints.

• Impression plasters in dentistry.

Other

• An alternative to iron oxide in some thermite mixes.

• Tests have shown that gypsum can be used to remove pollutants such as lead or arsenic from contaminated waters.

ยิปซัม (อังกฤษ: Gypsum) (CaSO₄·2H₂O) หรือเรียกว่าเกลือจืด เป็นแร่อโลหะที่มีความเปราะมากมีสีขาว ไม่มีสีหรือสีเทา มักมีสีเหลือง แดง หรือน้ำตาล เป็นมลทินปนอยู่ มีความวาวคล้ายแก้ว มุก หรือไหม ความแข็ง 2 ความถ่วงจำเพาะ 2.7 เนื้อแร่โปร่งใสจนกระทั่งโปร่งแสง อาจเรียกชื่อต่างกันออกไปตามลักษณะของเนื้อแร่ คือ ชนิดซาตินสปาร์ (satinspar) เป็นแร่ยิปซัมลักษณะที่เป็นเนื้อเสี้ยน มีความวาวคล้ายไหม ชนิดอะลาบาสเทอร์ (alabaster) มีเนื้อเป็นมวลเม็ดอัดกันแน่น และชนิดซีลีไนต์ (selenite) ใสไม่มีสี เนื้อแร่เป็นแผ่นบางโปร่งใส เกิดจากแร่ที่ตกตะกอนในแอ่งที่มีการระเหยของน้ำสูงมากและต่อเนื่อง ทำให้น้ำส่วนที่เหลือมีความเข้มข้นสูงขึ้น ถึงจุดที่แร่กลุ่มที่เรียกว่า “อีแวพอไรต์ (evaporites) ” จะสามารถตกตะกอนออกมาตามลำดับความสามารถในการละลาย (solubility) ซึ่งโดยทั่วไปเริ่มจากพวกคาร์บอเนต (carbonates) ซัลเฟต (sulphates) และเฮไลด์ (halides) การกำเนิด แร่ยิปซัมของไทยมีเนื้อเป็นเกล็ดเล็กๆ สมานแน่น เรียกว่า “อะลาบาสเตอร์ (alabaster) ” ซึ่งมิได้เกิดจากการตกตะกอนทับถมกันในสภาพการณ์ปฐมภูมิจากการระเหยของน้ำ แต่เกิดจากการเติมน้ำ (rehydration) ให้กับช่วงบนสุดของมวลแอนไฮไดรต์ จนเกิดการเปลี่ยนแปลง ชนิดแร่ ยิปซัมในประเทศไทยมีประวัติที่ค่อนข้างซับซ้อน และการศึกษาธรณีวิทยาแหล่งแร่พบว่า เคยผ่านการเปลี่ยนแปลงชนิดแร่ไปมา ระหว่างยิปซัมกับแอนไฮไดรต์ (CaSO4) หลายครั้ง (Utha-aroon and Ratanajarurak, 1996) ก่อนจะมีสภาพเช่นในปัจจุบัน